An insertion opening, which is generally closed by a locking blade, is required for the mounting of saddle-type rotor blades, which are often used in turbomachines with disk rotors. The locking blade is usually fastened by riveting the locking blade, or by the use of axial fixing pins. In order to ensure that the saddle fir tree root blades are seated without play in the peripheral direction during operation, the blades are mounted with prestress in the peripheral direction. The prestress selected, or operational effects, can have the result that removing the blades is only possible by destroying the locking blade.